Telephone switching system

Details Telephone switching system Telephone switching system

1978-05-18

1979-11-20

Claffy, Kathleen H.

179 81A, 1791708, H04B 320

Patent

active

041752180

ABSTRACT:
In the case where a two-wire circuit forming a trunk or a subscriber line of the two-wire system is converted by a hybrid circuit to a four-wire circuit of sending and receiving paths to form a transmission line between subscribers, if an impedance variation on the two-wire side is large, a leak from sending path to receiving path occurs and is amplified to cause singing. To eliminate the singing, a circuit for detecting the impedance fluctuation of the two-wire side is inserted in the two-wire circuit, and switching means inserted in the four-wire circuit is activated by an impedance detecting signal of the detecting circuit to electrically open the four-wire circuit, thereby preventing the singing phenomena. This method does not involve the use of an expensive attenuator which is troublesome to design for the prevention of singing.

REFERENCES:
patent: 3769466 (1973-10-01), von Pfeil et al.
patent: 3769466 (1973-10-01), von Pfeil et al.
patent: 3769466 (1973-10-01), von Pfeil et al.
patent: 3821494 (1974-06-01), Besseyre
patent: 3821494 (1974-06-01), Besseyre
patent: 3821494 (1974-06-01), Besseyre
patent: 4005276 (1977-01-01), Abramson et al.
patent: 4005276 (1977-01-01), Abramson et al.
patent: 4005276 (1977-01-01), Abramson et al.
patent: 4081616 (1978-03-01), Dumont
patent: 4081616 (1978-03-01), Dumont
patent: 4081616 (1978-03-01), Dumont

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